A forced-circulation type water-cooling system for a horizontal internal-combustion engine, disclosed in Japanese Utility Model Publication No. 1972-10583, is constructed as shown in FIG. 19.
In this system a cooler 110 such as a radiator is located roughly at the same level as an engine body 107 of a horizontal internal-combustion engine 106 in a lateral space outside the engine body 107. A water jacket 122 comprises a cylinder jacket 123 formed within a cylinder block 113 and a head jacket 124 formed within a cylinder head 117. Head jacket 124 is provided with a cooling water inlet 156 at the underside thereof and the cylinder jacket 123 is provided with a hot water outlet 158 at the upper portion thereof. The hot water outlet 158 and the upper portion of the cooler 110 are connected to each other by a hot water pipe 159, and the lower portion of the cooler 110 and the cooling water inlet 156 are connected each other by a cool water pipe 160. A water pump 162 is interposed in an intermediate portion of the cool water pipe 160 in a space under the cylinder head 117. The cooling water within the cooler 110 is adapted to be delivered under pressure through the cool water pipe 160 to the water jacket 122 and circulated through the hot water pipe 159 to the cooler 110 by means of the water pump 162.
The following problems are associated with said conventional construction.
(a) The size of an internal-combustion engine becomes large.
When the water pump 162 is located in a narrow space under the cylinder head 117, the lower portion of the water pump 162 cannot help projecting downwardly from the underside of the engine body 107. The overall height of the engine body 107 increases correspondingly so that projecting extent and the size of an internal-combustion engine 106 are enlarged.
(b) The supporting construction and an alignment adjusting arrangement for a water pump are complicated.
First of all, since a pump supporting frame (not shown) is required only for supporting the water pump 162, a supporting construction for the water pump 162 is complicated.
As for driving the water pump 162, the simpliest arrangement that a pump shaft is interlockingly connected to a crankshaft 134 of the engine body 107 through a wrapping connector such as a belt transmission means. For accomplishing the simplest arrangement, it is necessary to accurately adjust the pump input wheel fixed to the pump shaft in the axial direction of the pump shaft relative to the pump driving wheel fixedly secured to the crank shaft 134 projecting from the engine body 107 in the fore and back direction. In such a conventional construction, since it is required to mount the engine body 107 and the pump supporting frame separately on a common base, any mounting error in the direction of the pump shaft becomes significant. In order to correct such an error, an adjusting shifter means is required for adjustably shifting the water pump 162 in the axial direction of the pump shaft on the pump supporting frame.
Consequently, the supporting construction and the alignment adjusting arrangement for the water pump 162 become complicated.
(c) It is difficult to cool the entire cylinder head intensively.
Generally in a water-cooled horizontal internal-combustion engine, a head jacket 124 is provided with jacket communication ports 125 to interconnect the cylinder jacket 123 and the head jacket 124 at the upper and the lower portions in the middle of the fore and back direction thereof.
Since the cooling water delivered under pressure by means of the water pump 162 is adapted to be ejected upwardly through the middle portions in the fore and back direction within the head jacket 124 from the cool water inlet 156 and then the ejected upper water flows into the cylinder jacket 123 through the jacket communication ports 125 in large quantities, the cooling water flow through the fore and back opposite portions in the head jacket 124 is reduced and, as a result, it is difficult to perform intensive cooling throughout the cylinder head 117.
(d) The engine is subjected to a large thermal strain.
Since the fore and back opposite portions of the cylinder head 117 are not cooled enough while the middle portions thereof in the fore and the back direction are cooled intensively, a large thermal strain tends to be caused in the cylinder head 117 by a large temperature difference therebetween.